Microelectronic integrated circuits based on patterned semiconductor materials are continuing to evolve towards devices with an extremely high density of circuit elements per unit volume. As the features of these devices are reduced to smaller sizes, the performance of the materials that constitute the device will critically determine their success. Many integrated circuits (IC's) use aluminum, optionally including small amounts of other, alloying metals, as the conductor between the individual devices or structures that make up the circuit. It has been found that when aluminum is in direct contact with underlying silicon, so-called spiking, or migration of aluminum atoms into the silicon may occur which can interfere with the performance and reliability of the resulting IC device. Therefore typical aluminum interconnects include a layer of titanium over the silicon substrate, covered by a layer of titanium nitride and then the aluminum layer. The titanium nitride serves as a physical barrier to prevent migration of aluminum atoms into silicon and the titanium layer provides electrical connection to the underlying silicon substrate, tungsten plug, or aluminum layers. The stack may also include an additional TiN barrier layer over the aluminum conductor.
While the Ti/TiN/Al/TiN interconnect stacks have provided satisfactory results in the past, a key factor in meeting the enhanced performance requirements of improved devices is solving the problem of electromigration of aluminum atoms in the aluminum layer during operation of the device. Electromigration is directly related to the lifetime of the IC device. It is known that when the aluminum layer has a <111> crystallographic orientation, the electromigration problem is reduced. One approach to promoting formation of the aluminum layer in the desired <111> orientation is to form the TiN layer in a <111> crystallographic orientation. Methods for enhancing TiN <111> formation are described, for example, in a series of patents to Nulman et al. (U.S. Pat. Nos. 5,242,860, 5,360,996, 5,434,044, and 5,521,120). Further, it is known that enhancing the <0002> preferred orientation of the titanium underlayer promotes formation of the subsequently deposited TiN and Al layers in the desired <111> orientation and hence results in improved device performance. It would be desirable, therefore, to provide a deposition method that enhances the preferred orientation of a titanium film. It would further be desirable if the method is readily integrable with standard processes for deposition of aluminum interconnect stacks and is applicable to a variety of materials used in metallization layers.